An autoimmune chronic inflammatory disorder characterized by inflammation in the vertebral joints of the spine and sacroiliac joints. It predominantly affects young males. Patients present with stiffness and pain in the spine. The disease is ankylosing spondylitis (Monarch Disease Ontology entry MONDO_0005306). Also known as: Bekhterev syndrome, Bekhterev's disease, Marie-Strumpell disease, ankylosing spondylarthritis.